The present invention relates to a medicinal composition containing a tissue plasminogen activator (hereinafter referred to also as "t-PA"). In particular, the present invention relates to a t-PA or a modified t-PA-containing medicinal composition, characterized by containing t-PA or modified tissue plasminogen activator (hereinafter referred to also as "modified t-PA") and nicotinamide or a derivative thereof.
t-PA activates plasminogen to form plasmin which dissolves fibrin which is the main component of the protein substrate of the thrombus. t-PA preparations were developed as a thrombolytic agent having a very high selectivity toward the thrombus in the thrombolytic treatment for thrombosis which causes myocardial infarction and cerebral infarction. Further, various modified t-PA's were also produced by genetic engineering for the purpose of obtaining higher affinity to fibrin and the half-life in blood than those of the natural t-PA. The modified t-PA's thus produced from procaryotes are of non-glycosyl type unlike the natural t-PA. t-PA's are proteins generally extremely difficultly soluble in water. In particular, the modified t-PA's are more difficultly soluble in water than natural t-PA to make very difficult the preparation thereof and the preparation of injections or the like to be dissolved in water at the time of the administration to a patient, while the modified t-PA's have various advantages such as increase in the affinity to fibrin and elongation of the half-life in blood.
The basic idea in the recent treatment of acute myocardial infarction is that, when the coronary arteries are blocked up, the blood circulation is to be recovered as immediately as possible to minimize the cardiac disorder. According to this idea, a drug of a high concentration which can be safely administered in a short time is preferred. Therefore, when the recirculation of the blood in the coronary arteries in an early stage and the prevention of the blocked portion from the enlargement are expected in using the modified t-PA having the various advantages, it is preferred to immediately administrate the preparation having a high t-PA concentration once. Under these circumstances, the development of a t-PA preparation having an improved water solubility, high concentration and stable protein structure is demanded, even though t-PA's, particularly glycosyl-free t-PA's, are difficultly soluble in water and have an unstable protein structure.
In addition, t-PA's including the modified t-PA's are generally unstable to heat. To develop such substances usable as medicines, a technique for stabilizing them is also indispensable.
As for the prior technique for solubilizing t-PA, a technique wherein t-PA is solubilized and stabilized by adding arginine hydrochloride or a salt thereof to t-PA under neutral to weakly alkaline condition is known [see Japanese Patent Publication for Opposition Purpose (hereinafter referred to as "J. P. KOKOKU") Nos. Hei 6-72105 and 6-99324]. However, the defect of this technique is that the stability of the protein structure of t-PA in a high concentration is reduced under the neutral to weakly alkaline condition. As for the solulbility, the dissolving properties of the glycosyl-free t-PA and modified, glycosyl-free t-PA are different from those of the natural t-PA, and the redissolution of the self-associated t-PA by this technique has been difficult.
Further, a process for solulbilizing t-PA by controlling the solution at pH 2 to 5 is known (see J. P. KOKOKU Nos. Sho 63-38327 and Hei 3-69332). However, for obtaining the intended preparation, this process still has some problems to be solved because freeze-dried t-PA or a t-PA solution is rapidly decomposed and deactivated.
On the other hand, the following processes for stabilizing t-PA have been known in the prior art: a process wherein albumin is added (J. P. KOKOKU No. Hei 3-29390), a process wherein a decomposition product of albumin is added [Japanese Patent Unexamined Published Application (hereinafter referred to as "J. P. KOKAI") No. Hei 1-221325) and a process wherein gelatin treated with an acid is added (J. P. KOKOKU No. Hei 5-27607). However, it has been confirmed that the effects of these processes are unsatisfactory when the concentration of t-PA is high and that the solubility of t-PA in a citric acid buffer solution is reduced particularly by the addition of albumin.